1. Field of the Invention
This invention concerns a variable-capacity turbocharger. More specifically, it concerns an improvement of a nozzle unit for supplying exhaust gases to a turbine of the turbocharger.
2. Description of the Related Art
A turbocharger is an effective means to increase the output of an internal combustion engine. A turbine is rotated by the exhaust gas from the engine, and a compressor mounted on the same shaft as the turbine pressurizes the air supplied to the engine. Turbochargers are currently installed in a variety of engines. However, the flow rate of the exhaust gas varies with the speed of the engine""s revolution. The flow rate of the exhaust gas which is actually supplied from the engine will not always be that needed to produce the ideal operating conditions for the supercharger. To rectify this situation and allow the turbocharger""s capacity to be used to its best advantage, a variable-capacity turbocharger has been developed. In a variable-capacity turbocharger, the flow of the exhaust gas in the turbine compartment is regulated according to the operating state of the internal combustion engine.
This sort of variable-capacity turbocharger has a number of nozzle vanes on the nozzle unit of the turbine, which is inside a housing. FIG. 8 shows a partial cross section of the nozzle unit in a variable-capacity turbocharger belonging to the prior art.
In FIG. 8, turbine 228 is supported by bearings in a main housing of the variable-capacity turbocharger in such a way that it is free to rotate. The exhaust gas from the internal combustion engine flows into housing 220 through an intake port of the variable-capacity turbocharger. It is supplied to turbine 228 by way of scroll channel 226 which is formed in housing 220 and nozzle unit 210 which forms the inlet to the turbine 228. The exhaust gas supplied to turbine 228 is then exhausted through the exhaust port after it has driven the turbine 228.
Nozzle unit 210 comprises mounting plate 202, which is fixed to housing 220, and side plate 206, which is placed opposite mounting plate 202. A number of nozzle vanes 204 are placed at equal intervals along the circumference between the two plates. Side plate 206 is fixed to mounting plate 202 by supporting bolt 208, which goes through the plate 206. Nozzle vanes 204 have a shaft portion. They are mounted on mounting plate 202 in such a way that they are free to rotate with the shaft portion.
Because side plate 206 is fixed in place by support bolt 208, the heat of the exhaust gas which is supplied to the turbine raises its temperature, causing it to thermally deform. A space is provided between nozzle vanes 204 and side plate 206, as in FIG. 8, in order to prevent nozzle vanes 204 from catching or sticking during rotation and allow them to operate smoothly. This is why in variable-capacity turbochargers of the prior art a portion of the exhaust gas being supplied to scroll channel 226 is routed through the space between nozzle vanes 204 and side plate 206 and supplied to turbine 228 without going through the area around nozzle vanes 204. In the prior art design, then, because some of the gas is supplied to turbine 228 without passing through the channel around vanes 204, the efficiency of the variable-capacity turbocharger decreases.
This invention is to solve the shortcomings of the prior art design described above. The object of this invention is to minimize as much as possible or eliminate the quantity of exhaust gas supplied to the turbine without going through the channels between the nozzle vanes. This invention is also effective at minimizing the quantity of exhaust gas supplied to the turbine from behind the side plate without going through the nozzle unit.
A variable-capacity turbocharger which controls the opening degree of nozzle vanes has a turbine provided in a housing, which is free to rotate on a turbine shaft, a plurality of nozzle vanes arranged in nozzle units around the turbine in the housing, a link plate which rotates freely around the turbine provided in the housing, which is connected to the nozzle vanes by means of a plurality of levers, and which continuously moves the nozzle vanes synchronously between the open and closed positions, and an actuator outside the housing, which is connected to the link plate through a transmission mechanism. The turbocharger according to this invention is distinguished by the following features. It has a mounting plate fixed to the housing, and a side plate installed in a recess provided in the housing in such a way that the side plate can move in the recess, both of which are provided parallel to the turbine shaft. A pushing means pushes the side plate toward the mounting plate and a limiting means limits the movement of the side plate parallel to the turbine shaft toward the mounting plate.
The pushing means to push the side plate can be a pressure chamber created between the side plate and the recess, or a spring plate mounted between the side plate and the recess.
The side plate has a doughnut shape whose center is the turbine shaft. The recess has a diameter slightly greater than the diameter of the side plate, and the recess also has, on the inner surface, a round projection which protrudes parallel to the turbine shaft toward the side plate. The spring plate is engaged with and fixed to the round projection.